Stroke is the third leading cause of death in many industrial countries. Around 20% of the patients do not survive the first month and >30% who are alive 6 months later will be dependent on other people. Stroke is often ischemic and the majority of ischemic strokes are the result of an occlusion of a major cerebral artery by a thrombus or an embolism, which give rise to loss of blood flow in one or more specific regions.
Today there are two alternative ways for the treatment of stroke. One way is to try to establish reperfusion to the compromised region by dissolution of the clot using thrombolytic agents. Today, the recombinant tissue-plasminogen activator (rt-PA) is the only thrombolytic agent approved to be used for the treatment of acute ischemic brain injury. The use of rt-PA is restricted to administration within 3 hours after the stroke has occurred. However, its use increases the risk of haemorrhagic transformation, which limits its use. The second way is to develop compounds, which interfere with the biochemical pathway that leads to cell death. By such an approach the core area of injury will not be saved. However, the surrounding area called the ischemic penumbral area (or simply the penumbra) might be saved and the degree of damage restricted.
So far all the agents developed, which were supposed to save the penumbral area, failed to convincingly show efficacy in clinical trials despite they had shown good potential results in animal models. Examples of such compounds are NMDA receptor antagonists, Kappa opioid peptide receptor antagonists, NO inhibitors, Na+ channel blockers, K+ channel blockers, and cell membrane stabilisers, among others (O'Collons V E et al., 2006, 1026 experimental treatments in acute stroke. Ann. Neurol. 59; 467-477).
Other treatments are mainly focused on preventive pharmacotherapy, e.g., by use of antihypertensive agents, antilipids or anticoagulants. Current treatment also relates to alternate ways of cooling the patients, in order to mitigate the negative effect of a stroke. Therefore, recorded treatments are insufficient, or, they can be considered as supportive and synergistic to future regimens emanating from the present invention.
The past 20 years have focused on the mechanisms of ischemic brain damage within the brain tissue per se; the work is related to free radical-mediated damage (Chan P H, Reactive oxygen radical signalling and damage in the ischemic brain. J Cereb Blood Flow Metab 2001; 21:2-14), apoptosis (MacManus J P, Buchan A M. Apoptosis after experimental stroke: fact or fashion? J Neurotrauma 2000; 17:899-914), gene expression (Sharp F R et al. Multiple molecular penumbras after focal cerebral ischemia. J Cereb Blood Flow Metab 2000; 20:1011-1032), and inflammation (Iadecola C, Alexander M. Cerebral ischemia and inflammation. Curr Opin Neurol 2001; 14:89-94) all within the brain tissue/neurons (Wieloch T. Molecular mechanisms of ischemic brain damage. In Cerebral Blood Flow and Metabolism, ed by L Edvinsson and D N Krause, Lippincott Williams Wilkins, Philadelphia 2002, pp 423-451). In particular there has been a focus on NMDA receptors and calcium toxicity as a primary trigger in ischemia. This has been a target in pharmacology to search for the molecular mechanisms of ischemic brain damage and for neuroprotective compounds against ischemic injury. To date, however, no successful clinical stroke trial has appeared (Lees K R. Neuroprotection. Br Med Bull 2000; 56:401-412, O'Collons V E et al., 2006, 1026 experimental treatments in acute stroke. Ann. Neurol. 59; 467-477). In all the work during the past 20 years the main focus has been directed towards the molecular mechanisms within the brain neurons. A hypothetical vascular involvement is regarded as a passive secondary event that by and large has been left out from the discussions, probably because vasodilator drugs are inactive.
Acute focal cerebral ischemia (stroke) results in a severely ischemic core with low residual cerebral blood flow (CBF) whereas the ischemic penumbra synaptic activity is reduced while the residual CBF is enough to maintain membrane ionic gradients. In principle, nerve cells in the penumbral zone can be salvaged after a cerebral ischemic episode; most neurologists have witnessed this fact in the form of patients' recovery of normal motor function within 24 hours after acute hemiparesis. Such cases indicate the complex and variable nature of blood flow reduction in stroke as well as the potential to reverse events related to the penumbral zone after acute cerebral infarction. The expansion of depolarized core coincides with the occurrence of spontaneous peri-infarct spreading depolarization. The tissue viability threshold and its relationship to the penumbra has focused on electrical and membrane failure in brain tissue, and therefore, it has been suggested that the ischemic depolarization increases the metabolic burden, thereby exacerbates the energy deficit, and enlarges the infarct. This view has by and large neglected the fact that stroke primarily is a cerebrovascular disorder. Recently, data was presented that there is neurovascular vasoconstrictor coupling during the ischemic depolarization which contributes to the hemodynamic progression of damage in focal cerebral ischemia.
We have observed a rapid transcriptional upregulation of contractile endothelin-1, and angiotensin II receptors in vascular smooth muscle cells in the middle cerebral artery (MCA) leading to the ischemic region starting immediately after induction of the cerebral ischemia. These changes result in enhanced contraction of the vasculature leading to the ischemic region, particularly because agonists for these receptor are produced in the cerebrovascular endothelium. In agreement, single receptor inhibition has in the past only been found to have limited effect in reducing cerebral infarct size after focal ischemia. Therefore, we hypothesize that blocking the transcriptional upregulation of PKCα and PKCβ that are the key subtypes of PKC, or raf→MEK1/2→ERK1/2 that are involved in the MAPK pathways. We have in experimental work on first isolated brain vessels and then in vivo found that interaction with these protein kinases blocks the upregulation of vascular receptors specifically in association with the ischemic region. We have furthermore found that the two pathways PKC and MAPK ERK1/2 may interact (Ansar & Edvinsson, Stroke 2008). By specific blockade of either or both will reduce the cerebral infarct that occurs after focal cerebral ischemia and normalize the neurology deficit.
Consequently, there is a need for new agents to be used for the treatment of stroke as well as screening methods to enable the finding of new bioactive agents that can be used to efficiently treat ischemic brain injury, to save the penumbral area and help the patient to get a better quality of life. Today, such agents are not available, agents, which are safe, non-addictive and effective, and also to which the body in the long-term is not refractory.